Performance of structures as function arguments

Hi, I sometimes see code where structures are passed into a function and the fields are then stored in local variables, e.g.

function(data)

alpha = data.alpha [...]

Is there a good reason to do this, are the local variables accessed quicker than the structure elements or something?

Answer 1

[Iain]

Yes.

The "Good reason", is that an equation, say,

 L = 1/2 * rho * Vel.^2 * area * (alpha*P1 + P0);

Is far quicker to read and write than:

 Output.Lift = 1/2 * Environment.Density * Aircraft.Velocity.X.^2 * Aircraft.WingSurfaceArea * (Aircraft.Alpha * Aircraft.LiftCoefficientP(1) + Aircraft.LiftCoefficientP0)

Structures (particularly large ones, and arrays of structures) can be much slower than basic variables.

[Dan]

Ok thanks, i can see that this can be a reason. To clarify though, my interest was not in speed of writing or reading of code, but in Matlab reading structures (not arrays of structures) rather than basic variables.